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Re: [PATCH] x86-64: memcmp-avx2-movbe.S needs saturating subtraction [BZ #21662]
On 06/23/2017 01:52 PM, Florian Weimer wrote:
On 06/23/2017 10:48 PM, Richard Henderson wrote:
On 06/23/2017 06:51 AM, Florian Weimer wrote:
+ shll $8, %eax
+ shll $8, %ecx
+ movzbl -1(%rdi, %rdx), %edi
+ movzbl -1(%rsi, %rdx), %esi
+ orl %edi, %eax
+ orl %esi, %ecx
Do you really need to re-load and merge the final byte?
It would appear you could leave the low byte zero.
Sorry, I don't understand. Is this the same issue as H.J. raised and
The final/third byte certainly can affect the outcome of the comparison.
Obviously I didn't intend to imply that one can completely ignore the final
byte. From the larger context that I didn't quote, it appeared that the last
byte has already been loaded.
That said, I take it all back -- I mis-read the diff.